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Old 22nd December 2008, 06:47 PM   #11
j beede is offline j beede  United States
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Here's a photo of a mockup I have for one side.
...j
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Old 22nd December 2008, 08:29 PM   #12
Few is offline Few  United States
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A search on this site for stator insulation will yield a few approaches, but most folks are also trying to insulate the diaphragm side of the stator and therefore worry about how the insulation is going to affect the operation of the device. If you're just trying to insulate the user side of the stator while leaving the diaphragm side uninsulated, I would think you could get away with quite a variety of coatings. You might consider Calvin's advice in post #19 in this thread.

I know this is comment is likely unnecessary, but be quadruple sure that there's no way your new headphones are going to place the stepped-up amplifier output across your two ears. I once found a break in the sprayed on insulation on my ESLs while they were playing, and I discovered it the hard way. I had to wait for my fingers to recover before I could make good use of a screwdriver. I'd hate to hear somebody had a similar experience using their head. From your earlier posts I sense you're aware of the danger. I just don't want anyone else reading the thread to underestimate the risk.

By the way, the photo looks great! Nice work.

Few
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Old 23rd December 2008, 12:51 AM   #13
j beede is offline j beede  United States
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You know, I have enjoyed this headphone project and I have acquired and learned to use a few woodworking tools... That said, I am hesitant to move ahead given the risk that ES headphones inherently bring along with them. I often wonder how Koss, Stax, Jeckin, etc. survived their entries into the commercial ES headphone market.

Few, you experienced motor problems after discharging your stators? Scary. I was at Fry's yesterday and experienced a large static discharge when I touched an empty computer case. This was unlike any I have felt before--it felt like someone simultaneously hit both of my elbows with 16 ounce hammers. It took 3-4 minutes before I felt 100% again. I have never felt 2000-3000VAC at any current level, nor do I care to.

Any ES headphone builders out there have any thoughts to add?

Regards, j
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Old 23rd December 2008, 02:09 AM   #14
Few is offline Few  United States
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Hello j,
I don't mean to monopolize the bandwidth, I just want to balance my doom and gloom caveats with a post that's a bit more encouraging. I've long thought about making electrostatic headphones, so maybe it's just selfishness on my part, but I do hope you bring your project to fruition. It looks great so far and I don't think the safety issues are insurmountable. These devices are commercially available, after all.

You may not be too enthused about the idea of a grounded screen between the stators and your ears for fear of corrupting the sound, but it might put your mind at ease as you strap the suckers to your head the first time. I found some very open copper mesh (screen) at the McMaster-Carr site. I think if you had 1/4" holes through the screen, and ~70% open area (which is one of the options I think I remember) you're unlikely to hear much of an effect. If there were a few mm between the stator and the screen I think you could be quite confident you weren't going to reboot your brain when you fire them up. I think the screen cost about $14 for a square foot---a lot for screen, not much for brain safety. You could probably use much cheaper aluminum window screen as well. I just looked into the copper because you could solder a ground wire to it. Just a thought...

Best of luck, and I hope you keep at it! By the way, you can always do your initial listening tests at very low levels so that you can reassure yourself you've not designed a combination earmuff/bugzapper.

I'll now get out of the way so somebody who actually has experience with this sort of project can chime in.

Few
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Old 23rd December 2008, 06:49 AM   #15
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Hello J,

I finished my ES headphones last month, and they sound really wonderful. I used PCB as the stators and coated the copper side with paint. The highest voltage I had tried was around 1,200V, and I didn't have any problem putting them around my head. It was quite scary, though.

Your headphones look really nice. Please allow me to copy your idea to make the frames. They look awesome.

By the way, what is the thickness of the spacer you use?

Wachara C.
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Old 23rd December 2008, 07:25 AM   #16
j beede is offline j beede  United States
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Hello Wachara,
You used perforated PCB for stators? Copper clad on both sides and you used paint for safety insulation for the "ear" side and for the outside? This means no grounded safety "fake" stators? The PCB I have seen has very small holes, did you drill you own holes?

You are using 1200VDC for diaphram bias? or 1200VAC swing out of your audio transformers?

I have used 3/32" neoprene spacers and will use 1/16" on my next set of drivers. I am using 550VDC diaphram bias through 20 MOhms in series for current limiting.

I don't see much discussion here regarding personal safety and stator danger. Most of the stator coating discussions are focused on diaphram safety. I have owned commercial ESLs since 1975 and have never been shocked. I have never owned or used ES headphones before.
...j
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Old 23rd December 2008, 07:48 AM   #17
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Hello J,

I used a one sided PCB and I used my homemade CNC to drill holes on it. I painted only the copper side. Here is a link to my other forum . I'm very sorry that it's all in Thai, but you should get a general idea.

I can't find a better spacer, therefore I stick with the 1 mm PCB spacer. I now bias the stator to around 600V. However, I have made a switch so that I can choose to bias at either 600V or 900V. The voltage is fed into the faked center tap(just like yours) and out to the stators. The diaphragm is series with 20Mohm resister then to ground.

It's a very fun project and it's worth all the time and effort I've put in.

Wachara C.
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Old 26th December 2008, 05:28 AM   #18
j beede is offline j beede  United States
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Hello Wachara C.
The photos on the Thai website were much appreciated. I see that the example there is using larger diaphrams than I am. I am experimenting with different diameters. The spacers there also appear to much wider than mine, I am trying to produce as much radiating surface as I can with the small diameter stators I am using. I am hoping that loose diaphrams and 1.6mm spacers allow me to compensate a bit for my small 51mm driver diameter.
Do you use CNC to cut phenolic spacers?
Regards, j
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Old 26th December 2008, 06:13 AM   #19
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Hello J,

Yes, I used my CNC to cut all the stators, spacers, and the frames. The material for stators and spacers is a 1mm PCB. The outer frame is cut from 10mm plastic sheet.

Wachara C.
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Old 26th December 2008, 05:30 PM   #20
j beede is offline j beede  United States
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Quote:
Originally posted by Few
Hello j,

[cut]

You may not be too enthused about the idea of a grounded screen between the stators and your ears for fear of corrupting the sound, but it might put your mind at ease as you strap the suckers to your head the first time. I found some very open copper mesh (screen) at the McMaster-Carr site. I think if you had 1/4" holes through the screen, and ~70% open area (which is one of the options I think I remember) you're unlikely to hear much of an effect. If there were a few mm between the stator and the screen I think you could be quite confident you weren't going to reboot your brain when you fire them up. I think the screen cost about $14 for a square foot---a lot for screen, not much for brain safety. You could probably use much cheaper aluminum window screen as well. I just looked into the copper because you could solder a ground wire to it. Just a thought...

[cut]

Few
Hello Few,
If you look at the photo I posted above you can see the very open aluminum shield (painted black) that I made. Soldering to Aluminum is "iffy" at best, for me. I am ordering perforated steel from small parts to duplicate the shield, but in a material that I can solder to. Obviously I would rather not have to run the extra wire to each panel for the ground path. Since the shield will be isolated from the stator with a 1.6mm diameter silicone o-ring I am thinking that the charge built up on the shield is via ac coupling (per plan) or high resistance leakage path (unplanned). Either would be a potential annoyance, but should not be a hazard. That means grounding the shield should be unnecessary, agree? I will still make the shields out of steel in case I choose to ground them.

FYI--My Stax SR-44 arrived earlier this week and I gave them a listen last night for the first time. Not bad, full range, moderately uncomfortable, not a revelation. I think the hard, flat leather earpads are too thin--locating the diaphragm too close to the ear. The earpads make noise as they move on the outer ear. They are also heavily damped on the outer side making them behave somewhat like a closed design. Lightly covering the outer shield while listening makes almost no audible difference. Doing this with my Grado earphones produces a dramatic effect. If anything I am now more motivated to complete my ES headphones as I think I can do better than the (low end) Stax.

I should mention that I am not a serious headphone user. I have owned full range ESLs for many years and have always wanted to build a set of my own design. The headphone project was meant to be a dry run to start me moving up the learning curve.
...j
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